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Angular dependence of coaxial and quasi-coaxial monitoring systems for process radiation analysis in laser materials processing
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. JENOPTIK Optical Systems GmbH, System Development Advanced Manufacturing, Göschwitzerstraße 25, 07745 Jena, Germany.ORCID-id: 0000-0001-8601-2923
JENOPTIK Optical Systems GmbH, System Development Advanced Manufacturing, Göschwitzerstraße 25, 07745 Jena, Germany.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology IWS, Winterbergstraße 28, 01277 Dresden, Germany.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0002-3569-6795
2022 (engelsk)Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 155, artikkel-id 107050Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Process monitoring is becoming increasingly important in laser-based manufacturing and is of particular importance in the field of additive manufacturing [e.g. Laser Powder Bed Fusion (LPBF)]. Process monitoring enables a reduction of production costs and a lower time-to-market. Furthermore, the data can be used to create a digital twin of the workpiece. There are already many established processing head-integrated monitoring systems for such applications as the multispectral analysis of process radiation. However, the monitoring of complex signals in systems with F-Theta scanner lenses is very challenging and requires specially adapted optics or measuring sensors.

In this paper a potential arrangement for spectroscopy-based process monitoring in pre-objective scanning is presented. The process radiation was monitored using a coaxial and a quasi-coaxial observation system. The measurements were carried out on both a solid and a powder coated sample of 2.4668 (Inconel 718) to show the potential use of these systems in laser-based additive manufacturing. In order to obtain comprehensive data about the process signal, the process zone was analyzed at different angles of incidence (AOI) of the laser using a high-speed camera (HSI) and a spectrometer. The connection between the HSI and the spectral measurements is discussed. The ionization of the material and the formation of a plasma was observed and found to lose intensity as the angle of incidence increases. A model of the system that demonstrates the intensity of the emitted radiation of the plasma was created. It enables the measured values to be corrected. The corrected measurement data can be used to detect impurities or a non-ideal energy input across the entire processing field, which is a move towards robust process monitoring.

sted, utgiver, år, opplag, sider
Elsevier, 2022. Vol. 155, artikkel-id 107050
Emneord [en]
Laser scanner, Process control, Laser powder bed fusion, Laser welding, Spectroscopic measurements, Monitoring techniques
HSV kategori
Forskningsprogram
Produktionsutveckling
Identifikatorer
URN: urn:nbn:se:ltu:diva-90062DOI: 10.1016/j.optlaseng.2022.107050ISI: 000819874000003Scopus ID: 2-s2.0-85127174513OAI: oai:DiVA.org:ltu-90062DiVA, id: diva2:1649206
Merknad

Validerad;2022;Nivå 2;2022-04-04 (hanlid)

Tilgjengelig fra: 2022-04-04 Laget: 2022-04-04 Sist oppdatert: 2022-07-15bibliografisk kontrollert
Inngår i avhandling
1. Spectral analysis in laser powder bed fusion
Åpne denne publikasjonen i ny fane eller vindu >>Spectral analysis in laser powder bed fusion
2022 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
Alternativ tittel[sv]
Spektralanalys vid laser powder bed fusion
Abstract [en]

This thesis is about the investigation of the spectral interaction of electromagnetic radiation with metal powders. For this purpose, spectral data of powders for laser powder bed fusion processes are investigated in three papers using different techniques. In paper A the spectral radiation behavior of the laser interaction zone is considered, in paper B and C the absorbance behavior of different metal powders depending on their state and measurement method.  

Paper A investigates the spectral signal of the process light generated by laser material interaction in laser powder bed fusion. The detection is performed by a coaxially guided measuring beam and a quasi-coaxial measuring beam simultaneously guided by another scanning optics. The signal characteristics depend on the angle of incidence of the measuring beam to the laser material interaction zone. Using high-speed recordings and optical simulations, a model for describing the signal behavior could be determined. The measured spectral intensity distribution representing the degree for energy coupling can be corrected with a correction factor over the whole field for solid materials. This correction includes a function describing the numerical aperture of the measuring channel and the laser intensity on the working field. For the investigated powder, the measurement signal fluctuated strongly and no transferable model could be formed. The reason for this was the different absorbance behavior of the powders investigated. Paper B therefore deals in detail with the spectral absorbance behavior of metal powders for additive manufacturing. Using a high-precision spectrometer, 39 powders were measured reflectively over a wide spectral range and the absorbance determined. By varying the degree of use, aging, grain size and impurities, various influence parameters are determined experimentally and discussed theoretically. Based on 20 derived laser wavelengths, technically usable wavelengths with better process efficiency and stability are proposed. From the obtained absorbance, the efficiency of energy coupling can be estimated and form a broad data base for the optimization of laser parameters. In order to perform the absorbance determinations also in situ in a laser powder bed fusion system paper C describes a possibility of an inline absorbance determination by high resolution coaxial imaging. A method is discussed for geometrically correct and gapless imaging of the processing plane, recorded through the laser optics. By imaging at six different wavelengths, metal powders can be distinguished by their absorbance spectrum and impurities can be detected. In an experimental implementation the functionality of the method is proven. The results are validated by optical simulations, ray tracing and comparative measurements with a high-precision spectrometer.

sted, utgiver, år, opplag, sider
Luleå: Luleå tekniska universitet, 2022. s. 200
Serie
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Emneord
Spectral monitoring, Laser powder bed fusion, Laser optics, Absorbance
HSV kategori
Forskningsprogram
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-90525 (URN)978-91-8048-098-7 (ISBN)978-91-8048-099-4 (ISBN)
Presentation
2022-06-16, A109, Luleå university of technology, Luleå, 09:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2022-05-10 Laget: 2022-05-09 Sist oppdatert: 2022-05-26bibliografisk kontrollert

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Brandau, BenediktBrueckner, FrankKaplan, Alexander F. H.

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